Stanley Arms was the registered trade name of the Wiebusch and Hilger Company of New York on firearms they retailed. It is widely held that these guns were produced in Belgium by F. Dumolin & Co.

http://www.littlegun.be/arme%20belge/art...%20cie%20gb.htm

It would have been produced from about 1908 to the mid-1920's. It should not be used with modern loads.

Pete